The present invention relates to a film forming apparatus for forming a film on a workpiece by using arc discharge.
The film forming apparatus disclosed in Japanese Laid-open Patent Publication No. 2016-20518 is a device that forms a film by depositing, on the surface of a workpiece, metal ions that have been released from an evaporation source by arc discharge. This film forming apparatus has a cylindrical evaporation source having an internal space for accommodating a workplace, a closing member for sealing the internal space, and an electrode provided along the inner wall surface of the evaporation source.
In such a film forming apparatus, the external power supply applies a discharge voltage to the evaporation source. The bias supply applies a bias voltage to the workpiece accommodated in the internal space of the evaporation source. The closing member is grounded. Then, the striker is brought into contact with the evaporation source and separated from the evaporation source immediately thereafter, so that arc discharge is generated in which the evaporation source serves as a cathode and the closing member serves as an anode. As a result, a high-density current is concentrated on the arc spot on the inner wall surface of the evaporation source, and ions are released. In the film forming apparatus described in the above publication, the electrode is either grounded or supplied with a positive voltage lower than the voltage of the evaporation source so as to function as an anode like the closing member.
In the case of the film forming apparatus described in the above publication, the electrode has a gas passage for supplying process gas to the internal space of the evaporation source. The metal ions released from the evaporation source are deposited not only on the workpiece but also on the electrode in some cases. In this case, if arc discharge is repeatedly generated and the deposition amount of metal ions on the electrode is increased, a metal film may be formed so as to block the opening of the gas passage in the electrode. Since the film forming apparatus of the above publication does not take these factors into consideration, there is still room for improvement.